1. Field of the Invention
This invention is related to the field of packages for Microwave Circuits, especially in the frequency band from 20 GHz and higher.
2. Prior Art
In the growing market of Personal Communication Services there is the need for low cost, wideband, surface mounted, reliable, user friendly packages for Microwave Monolithic Integrated Circuits (MMIC) and other devices. Applications are already identified at 23, 28, 32 and 38 Ghz and the industry is approaching production within the next two years. There are also applications identified at 60, 70 Ghz and higher frequencies. The applications are based upon Gallium Arsenide MMIC's chips. These IC devices have been packaged using complex, high reliability, high cost packages, designed for low volume assembly.
Existing packages are Surface Mounted but they are predominantly leaded, and employ expensive materials. Extensive use is made of glass to metal seals, multilayer ceramic structures, machined metallic cases or substrates, expensive alloys (Cu--Mo, Kovar, CuW and others) and relatively thick gold plating.
Prior art packages use for their design and construction a mixture of several of the following: stripline, microstrip, coaxial, pseudocoaxial and coplanar waveguide transmission line structures. Therefore, achieving the desired bandwidth of the packages is more the result of educated guessing than a truly designed structure. Examples of such packages are described in a U.S. Patent to C. Mattei, et al, U.S. Pat. No. 4,276,558 to P. T. Ho et al, U.S. Pat. No. 5,014,115 to L. J. Moser and U.S. Pat. No. 5,450,046 to Y. Kosugi et al. Some truly wideband packages, up to 40 Ghz, like Dielectric Laboratories, Inc. DiPak Model 20001, or StratEdge's Models SEC-580234, and SEC-580231, available today are complex and expensive to build. DLI's package requires a cavity created in the mother PC board and wirebonds or ribbon bonds from the package containing the IC to the surface of the mother board. As is appreciated by one of skill in the art, wirebonds are fragile and need to be protected from the environment. Additionally, the length of the wirebonds must be precisely controlled for high frequency operation. The foregoing adds cost to the overall assembly. Also, conventionally attached and configured wirebonds introduce discontinuities in the electromagnetic field distributions and RF current configurations. Those discontinuities need to be "tuned-out" in prior art packages to eliminate signal reflections and losses that would otherwise be damaging to the performance of the package.
The StratEdge.RTM. packages have large tabs for installation or require wirebonds from the package to the mother PC board. Additionally, these packages occupy large areas of mother PC board and are therefore not desirable.
Because of the materials and precision of manufacturing required, present wideband package designs are not conducive to high production volume, standardization, miniaturization and portability while maintaining low cost.
Other limited bandwidth packages, such as Microsubstrates Corporation Via/Pak 224Z, 218Z and 220A, and those of Kyocera Corp., have similar characteristics to the packages from DLI and the StratEdge packages.
With the shift of MMIC's from high cost specialty applications to more mainstream commercial applications, the existing packages are very inadequate, for reasons of cost, difficult assembly, and difficulty regarding testing for both packages alone and after being fitted with the MMIC. The above drawbacks must be overcome to meet the growing demand for microwave radio applications, such as PCS and LMDS, for low cost, small size, and portability.
The deficiencies and limitations of the above package are eliminated or greatly alleviated by the present invention.